This invention relates generally to security or subscription television systems and more particularly, it relates to a method and system for encoding and decoding of standard television signals thereby enabling reception thereof in an intelligible manner only by authorized subscribers.
Generally, there are known in the prior art various types of secure subscription television systems in which television signals are transmitted in a coded form for use only in subscribers' receivers having proper decoding means. In these systems, the coding is accomplished by modifying the sound and/or video portions of the television signals rendering them unintelligible or unpleasant to nonsubscribers or to subscribers who had not paid a fee to the broadcaster.
In these proposed secure subscription television systems, upon decoding the modified television signals, it was generally required that the precise modification signals must be removed or any missing signals must be generated and added to the modified television signals to produce a restored video as similar as possible to its original quality. Problems existed in these techniques due to the fact that the quality of the picture was generally subject to degradation and/or that difficulties were encountered in maintaining critical phase and other signal relationships in restoration.
The effectiveness of the secure subscription television systems is measured by the degree of success which it has in deterring unauthorized viewers from watching the modified television signals transmitted and in preventing the duplication of the decoding means.
It has also been experienced that in general the decoding technique utilized in the prior art systems could be easily duplicated by many resourceful viewers and thus defeat the security thereof. It would, therefore, be desirable to provide a method and system for encoding and decoding television signals in which maximum security is achieved and which will effectively deter unauthorized viewers in attempting to defeat the security. Moreover, it is needed to provide a system such that the theft thereof will be of little use or value.
In addition, the prior secure subscription television systems have a disadvantage in that none of them possess a positive and continuous control means for controlling automatically the decoder at the various subscriber stations whereby any or all of the decoders become selectively disabled or "locked out" if it does not receive the appropriate control signals from the broadcaster periodically before a pre-determined interval of time has elapsed. Thus, it would be desirable to provide a method and system for encoding and decoding of standard television signals in which the decoder at the subscriber's station are dependent continuously upon control signals transmitted by the broadcaster. In the absence of the periodic control signals, the decoder will automatically and rapidly become disabled rendering it essentially useless without the necessity of physically traveling to the subscriber's location.
It would also be suitable to provide in connection with a subscription television system means by which the subscribers could select the programs desired in a short time in advance of telecasting in a simple and easy manner. To this end, telephone communication circuitry can be provided so that the subscribers can request their programs to the broadcaster via a telephone interface which will transmit the subscriber's request to the broadcaster automatically without any great effort on his part other than by simply depressing a button at the subscriber's site. The telephone interface would automatically dial the broadcaster's telephone number, transmit the subscriber's unique account code to a computer at the broadcaster's site, and thus make possible the program selection by the subscriber at any time prior to the broadcast. Further, this would allow the system to be very reliable and substantially maintenance-free after the initial installation since all the control signals are done via over-the-air transmission and requests for service are done electrically on the telephone interface. There is eliminated the need to physically travel to the subscriber's location during normal use so as to supply or retrieve coins, cards, or tapes and the like for billing purposes as encountered in some prior art systems.